Bifocal lens



M. A. LAABS ET AL BIFOCAL LENS Filed Sept. 22, 1922 F/GI - INVENTORMAXA.LAA'BS HEW I v BY ATTORNEYS Patented May 19, 1925.

UNITED STATES PATENT OFFICE.

MAX A. LAABS AND HARRY W. HILL, OF SOUTHBRIIDGE, MASSACHUSETTS,ASSIGNORS TO AMERICAN OPTICAL COMPANY, OF SOUTHBRIDGE, MASSACHUSETTS, AVOLUN- TARY ASSOCIATION OF MASSACHUSETTS.

BIFOQAL LENS.

Application filed September 22, 1922. Serial No. 589,809.

To all whom it may concern:

Be it known that we, MAX A. LAABS and HARRY IV. HILL, citizens of theUnited States, residing at Southbridge, in the county of Worcester andState of Massachusetts, have invented certain new and usefulImprovements in Bifocal Lenses, of whlch the following is aspecification.

This invention relates to improvements in lenses and more particularlyto a division of our application filed September 19, 1921,

Serial #501,650 and has reference to improved construction of bifocallenses.

One of the principal objects of the present invention is the productionof a novel and improved form of bifocal lens formed from two parts ofglass in which the segment may be placed on the inner in place of theouter side, and in which the entire lens may be ground extremely thinwithout danger of damaging the segment of reading portion thereof.

A further object of the present invention is the provision of a lens ofthis character in which the size and shape of the segment may be largelyvaried as desired in the initial process of production, and in whichwastage of glass in production of the lens is reduced to a minimum.

A further object of the invention is the rovision of an improved form oftwo part bifocal lens in which the position of the centers of thedistance and reading portions in the finished lens may be. readilycontrolled and in'which the lens may be made of either monocentric orbicentric form as may be preferred.

Another object of the invention is the provision of an improved form ofblank for producing lenses of this sort which shall be in what may betermed semi-finished condition when put out by the manufacturer, and inwhich the segment may if desired be left for further. grinding so thatthe prescription grinder may adjust the position of center of thereading portion according to his personal ideas in respect thereto.

Other objects and advantages of the present invention should be readilyapparent by reference to the following specification taken in connectionwith the accompanying drawings, and it will be understood that anymodifications in the specific details of construction or steps inproduction may be made within the scope of the appended claims withoutdeparting from or exceeding the spirit of the invention.

Figure I represents a plan View of a completed blank for a pair oflenses before separation. v

Figure II represents a sectional view as on the line IIII of Figure I.

Figure III represents a View similar to Figure VII represents a planView illustrating the cutting out of an individual lens subsequent togrinding.

Figure VIII represents a view of the blank of Figure I split beforegrinding of the segment.

Figure IX represents a View of a method of grinding which may beemployed to advantage in connection with the grinding of the blank ofFigure VIII.

Figure X represents a perspective view of a monocentric typeof bifocalproduced iigm the blank ground as shown in Figure Figure XI representsa-plan view of a pair of blanks such as used in Figure I showing mostclearly the centering marks and flat edges molded on the initial blanks.

In the drawings, in which similar characters of reference denotecorresponding parts throughoutthe several views, the numeral 1designates the base blanks intended to form the distance portions of thebifocal lenses, these blanl sf's having the upper sur' faces 2 finishedto the desired curve which may for example be a minus 6 curve, thisbeing one standard .curve very widely used for the ocular side ofmeniscus lenses. These blanks, as indicated in Figure XI, are preferably molded with a flattened port-ion 3 at one side and with a slightnotch or nick as at L, the blanks when being fused being placed with theflat edges-in engagement with each other and the nicks corresponding toproduce a diamond shaped aperture, as is indicated in Figure XI. 1 Thelenses having been finished anglplaced to ether as indicated in Figure alarge isc or segment portion 5 is then placed resting upon the curves 6,this disc being of circular form the glass may be sub ect to a heatinsufficient to soften or affect the surface of the blanks 1S0 thattheir polished surfaces will be unaffected but the heat will provesufficient to soften the member 5 and cause it to drop from the positionshown in Figure II to the position shown in Figure III and firmly unitewith the surface 2 making the parts integral one with the other.

We have found it of particular advantage in this connection to initiallymake the member 5 with its under surface flatter than the curve 2 andwith its upper surface strongly curved to such a degree that after thesoftening of the parts the glass will be found to have bent to conformto the lower curve and securely unite therewith and a correspondingflattening of the upper surface will have taken place so that it willhave dropped to substantially the curve which is to be subsequentlyproduced thereon, thus minimizing the amount ,of grinding to be laterperformed. This also has'the advantage that a relatively thin edge isproduced as at 18 which satisfactorily bears against the supportingblank and will very readily unite therewith while the heavier centerportion will pull-itself down into close en- .gagement' with the glass.The advantage in mounting lenses on substantialy round blanks such asshown in Figure I resides in the fact that there is a space at each sideas at- 9 where the segment is not supported, leaving an open passageunder the segment through which the air can escape so there isv nodanger of bubbles or the like interfering wlth the fusing and the-partswill fuse one tothe other. It is important that the disc 5 be properlypositioned on the blanks 1.-

This is done by making a small drill spot, as at 10, in the disc 5 whichis mounted directly over the diamond formed by the nicks 4. It will beunderstood that any other system of lining up the parts equivalent tothis maybe employed so long as the disc is centered over the blanks sothefinal outline of the segment on the blanks will be the same.

In Figures IV and V we have illustrated a slightly different method offorming or uniting the parts. We make use of a -single large disc member11 having the central kerf or groove 12 formed in its finished surfaceto afi'ord an outlet for the air. This groove is .sufliciently narrowbut deep, so that the softening segment will come down against the faceof the blank 11 but will not close up the groove. A permanent air outletis thus provided at this point. This form of construction isparticularly adapted to be subsequently ground as by the grinding tool13 of Figure VI before the blank isseparated, the grinding beingcontinued until the shoulder at 14 is brought down to within a fewthousandths of an inch of the surface of the glass, when the readingportion of the lens is preferably considered finished. It is possible ifdesired to continue the grinding until the surface is brought even withthat of the major blank so that it blends therewith or is broughtslightly below the surface of the major blank, but we have found thatbest results can be line.

While the blanks can be mosteconomically surfaced two at a time andbefore-separation, if preferred the blanks may be first split as isshown by the individual blank in Figure VIII, and then subsequentlyground either substantially parallel with the slirface of the discs orreading portion, as shown m Figure VI, or grinding the segment a???at-an' angle, as is indicated in Figure leaving a higher shoulder at 15than at the:

lower edge as at the point 16, the advantage of this being that aprismatic effect is introduced counteracting the natural prism of anon-bifocal lens, to the end that the center of the reading portion willbe raised toward the geometrical center of the blank and if desired maybe so positioned that the'lens as an entirety in its finished form willbe amonocentric instead of a bicentric bifocal. This may be done eitherin the original process of manufacture or by the prescription grinder,as may be preferred, in the :so that there will be a prismatic balancein the two segments.

While we have referred to the segment and major portion of the blank asbeing formed from glass having different indices of refraction, such ascrown and flint, it is to he understood that our invention is alsouseful in those instances where both the major and minor portions arethe same, or substantially the same ndex of refraction,

- produced leaving a shoulder a few thousandths of an inch in height atthe dividingunite therewith the segment through thealthough the segmentis preferably of a glass having a lower softening point. This advantageresides in the fact that the major portion for a plurality of blanks maybe satisfactorily provided With itsfinal surface on the bifocal side,and We may then heating action and subsequently have it ground andpolish the segment only, a much distance or larger part of the blank ina circular zone or area about the central port1on.

We would also call attention to the fact that while We have referred tothe parts as being fused together they might in some cases be united bya cement or heat actuated cement and that the heating action may i notnecessarily be an actual fusion but and a segment secured to the majorportion over said vent.

2. A multifocal lens blank comprising a said easier proposition informing a lens of this sort than to have it ground and polish the majorportion having a continuous curve formed on one side and having a ventformed therein and a segment secured to .the major portion on the sidehaving a continuous curve and over said vent.

. 3. A 'multifocal lens blank'compr-ising a major portion having a venttherein and a segment fused to the major portion over the vent. 4. 'Amultifoc'al lens blank comprising a major portion having a vent thereinand.

a segment having an indexof refraction different from that of the majorportion 1 fused over the said vent.

5. A multifocal lens blank comprising a major portion having acontinuous curve formed on one side and having a vent therein'and asegment having an index of refraction different from that of the majorportion fused to the major portion on the side having a continuous curveand over the said vent.

6. A multifocal lens blank comprising a major portion having a ventformed therein and a segment fused to the major portionover said vent,the outer surface of the segment having a different curvature than theadjacent surface of the major portion.

HARRY W. -HILL. MAX A. LAABS.

